The invention relates to a valve for the intermittent introduction of fuel, in particular gaseous fuel, into an intake tube of an internal combustion engine.
When not only gaseous fuel such as hydrogen, but liquid fuel as well, is blown in, or insufflated, intermittently, if optimal combustion is to be attained, the course of the insufflated quantity S.multidot.Q.sub.k dt and the time .multidot.Q.sub.k should be a similar course at full rpm to the inflow of the air quantity .multidot.A.sub.L into the engine cylinder as shown in FIG. 1, in which curve V represents full-load operation, and curve T, in dashed lines, represents partial-load operation.
In current widely used injection systems (such as the L-Jetronic with intermittent injection), in every operating mode the valves are switched over between two fixed stops. In the open position of the valves, .sup..multidot. Q is constant. During idling, the opening time must in each case be very short, so that despite small full-load cross sections, it is difficult to determine small quantities precisely. These conditions are shown in FIG. 2 for full-load and partial-load operation. It has already been proposed that with liquid fuels as well, the upper stop in a ballistic valve seat be omitted. The result then is a quantity characteristic as shown in FIG. 3. With a smaller injected quantity, .sup..multidot. Q.sub.k and to a slight extent t are smaller; this is attained by correspondingly shortening the time during which voltage is applied. In the known injection systems that have been reduced to practice, however, only the time is varied, so that dynamic disadvantages would arise in these ballistic systems. It would be possible to lengthen the required stroke, but for these reasons these systems have not gained a foothold in practice.
By "ballistic" what is meant is that the movable valve closing element, on excitation of the magnet coil, makes an opening movement that is not limited by a stop, so that depending on the intensity of the electromagnetic excitation, the valve closing element is moved more or less in the opening direction of the valve and reverses its motion before reaching a stop, as a result of gravity and the force of the restoring spring. That is, similarly to a bullet, the movable valve element executes a motion similar to a ballistic curve.
If it is desired to adapt the introduced fuel quantity to the course of air quantity as shown in FIG. 1, then by comparison with previous injection systems, in which the valve may be opened virtually 100% at full load, the same quantities must be introduced within much shorter insufflation times. With gaseous fuels, considerably larger cross sections, at approximately the same pressures, must additionally be made available by comparison with liquid fuels. The kinetics of the known valves would be very critical then, especially since the damping and lubricating action of liquid fuels would not be available.
From diesel injection, systems are known in which the chronological metering is effected via a rotation in synchronism with the camshaft. A first diaphragm system on the jacket of a circular cylinder is rotated counter to a second diaphragm system. Once the first diaphragm system is located over the second one, at a suitable angular position of the camshaft, the valve is completely opened. In the usual diesel injection pumps, the quantity is defined via the pumping rate of the piston, so that the filling per stroke is the same. In the injection systems applicable here for Otto engines, however, a constant pressure difference over the diaphragm exists, and as a result the insufflated quantity per filling in these systems is inversely proportional to the rpm. To correct this behavior would require enormous effort.